Pultrusion is the term used to describe continuous pulling of fiber tows or rovings through a resin for impregnation, through a heated die for polymerization, and to a cut-off station for cutting the pultruded structure to desired lengths. Pultrusion processes, using reinforcements of fiberglass, graphite, and aramid fibers, and thermosetting resins, are well known, and are commonly referred to as "conventional pultrusion", while pultrusion processes using thermoplastic resins are very rare.
One disadvantage of thermosetting resin pultrusion acquired structures is the inability to reform or reshape a structure after it has passed through the process, due to the inability to reverse the cross-linking of the resin molecules in the process.
Another disadvantage of thermosetting resin use in pultrusion is the necessity of noxious and hazardous chemicals and solvents employed in the process ingredients. These materials include monomers and reactants such as styrene and methylenedianiline, and others.
The solvents used in some processes for thermoplastic pultrusion such as methylene chloride, chloroform, dimethyl formamide, and normal methyl pyrrolidone, employed in dissolving thermoplastic polymers prior to impregnating fibers in slurries and solutions, also present problems.
Another disadvantage of presently used thermoplastic pultrusion methodology is the inability to achieve an optimum fiber to resin volume ratio, and thereby maximize mechanical strength, specifically compression, flexural, and tensile strengths in the pultruded structure.
Other disadvantages of thermoplastic pultrusion products and processes is the inability to thoroughly wet-out fibers, thereby causing voids in resin starved areas; the cost of using prefabricated tow preg or prepreg tapes; and the limit to available lengths of these materials since they are generally manufactured by venders outside of the pultrusion industry and not available in lengths customarily employed by the pultrusion industry.
It is an object of the present invention to provide an improved apparatus and process of producing continuous fiber reinforced thermoplastic structural profiles or shapes that eliminate or minimize the disadvantages of the prior art thermosetting and thermoplastic pultrusion processes.
Another object of the present invention is to provide thermoplastic structural profiles or shapes that are essentially void free, and can be reshaped or post fabricated into additional shapes and structures by applying heat and pressure.
An additional object of the present invention is to provide an improved pultrusion apparatus and process that can employ, either recycled thermoplastic, such as polyethylene terephthalate from recycled plastic soft drink bottles, or unused or virgin resins.
A further object of the present invention is to provide an environmental friendly, improved hot-melt pultrusion apparatus and process that operates without solvents or hazardous chemicals and generates no noxious fumes.
Another object of the present invention is to provide an improved, cost effective pultrusion apparatus and process for producing continuous long length fiber reinforced thermoplastic structures that may be cut to the desired lengths or stored on or transported on spools.
Another object of the present invention is the production of fiber reinforced thermoplastic structures that may be fabricated into tension cables for bridges, retaining walls, and reinforcement bars in concrete and suitable for use in corrosive environments and earthquake sensitive areas.
An additional object of the present invention is an improved heated resin impregnation vessel for impregnating multiple tows of fiber in a hot-melt thermoplastic pultrusion process that insures through resin wetting and impregnation while maintaining a uniform resin flow and eliminating overheating and charring of the resin.
A still further object of the present invention is an improved resin melting and delivery vessel as a component part of a pultrusion apparatus.